1. Field of the Invention
The present invention relates to a process for production of cyanoacetates and, more specifically, to an esterification process for producing cyanoacetates by reacting crystalline cyanoacetic acid, or its concentrated pure 90% aqueous solutions, with a C.sub.3-12 alkyl, substituted alkyl, alkenyl, or cycloalkyl alcohol.
2. Description of the Prior Art
Cyanoacetates are important intermediates in the manufacture of cyanoacrylates, agricultural chemicals, cosmetics, pharmaceuticals, and a variety of other commercial and industrial products. There has been a continuing interest in the preparation of cyanoacetates from higher alkyl esters of cyanoacetic acid. As used herein, "higher alkyl esters" shall mean C.sub.3 -C.sub.12 compounds.
For example, Yonezawa et al., have reported on the manufacture of alkyl cyanoacetates by the esterification of cyanoacetic acid with alcohols in the presence of sulfuric acid as a catalyst in an article entitled ".alpha.-Cyanoacrylates III: Esterification of Cyanoacetic Acid and Monochloroacetic Acid", Yuki Gosei Kagaku Kyokai Shi 24 (7), 580-7 (1966). The addition of benzene was required to effect the azeotropic removal of water that is produced during the esterification reaction.
A procedure similar to that reported by Yonezawa et al. for the preparation of alkylcyanoacetates was later reported by Abdurakhimov et al. in "Cyanoacetate Esters", Tr. Tashk. Politek. Inst. (1973), 91 35-40 (Russian).
A process to make methyl and ethyl cyanoacetates was described by Mendow in "A Continuous Esterification of Substituted Acetic Acid with Aliphatic Alcohols," East German Patent DD 127117 770907 (1977). However, the process as disclosed is of little commercial interest since the recycling of unreacted alcohol is complicated by the presence of additional solvent that is involved in the process.
A modification of the foregoing process, namely, the use of a reactant as a solvent is disclosed in published German Patent Application 19617991.2 dated May 4, 1996. However, this approach is limited to alcohols with 3 carbon atoms or less, while the practical utilization of the process is further limited to methanol. As a further disincentive to the commercialization of this process is the requirement for specialized apparatus for conducting the reaction in a number of stages.
A process for esterification of cyanoacetic acid in an aqueous medium in disclosed in U.S. Pat. No. 5,347,032. The aqueous medium is comprised of an aqueous solution of cyanoacetic acid, which in a preferred embodiment is introduced as the crude stream directly from the acid synthesis. Although all of the examples are limited to butanol, it is disclosed that from 5 to 30 moles of a C.sub.4 to C.sub.10 alkanol are to be added per mole of acid in the aqueous medium. The process of the '032 patent thus requires a reaction vessel and related equipment capable of handling a large excess of water and alcohol, even before the reaction is commenced. In addition to the large-capacity equipment requirement, substantial utilities must be expended in heating and distilling off the water-alcohol azeotrope in order to drive the esterification reaction towards completion. The use of a crude acid synthesis stream will also produce undesirable impurities, such as esters of various mono- and dicarboxylic acids, as well as inorganic salts, in the reaction mixture with the cyanoacetate product.
A process for producing both butyl cyanoacetate and cyanoacetic acid is disclosed in U.S. Pat. No. 3,668,231 to Rosin et al. This patent discloses a process for the synthesis of cyanoacetamide in which an alkyl cyanoacetate is formed as an intermediate. Cyanoacetic acid is prepared as an aqueous solution without removing any of the inorganic salts produced. Water is present in such a relatively small amount that the concentration of salt in the reaction mixture is high so that the reaction mixture is virtually insoluble in a higher alkanol such as n-butanol, thereby permitting use of the higher alkanol to extract the cyanoacetic acid from the mixture. Following extraction of the cyanoacetic acid from the reaction mixture, the substantially water-free cyanoacetic acid reacts to esterify the alkanol in the presence of an esterification catalyst. During the course of the reaction, the water of esterification and lower alkanol are removed as an azeotrope. The process of the '231 patent is relatively complex from a commercial standpoint and not economically viable since it produces undesired by-products in relatively large quantities that must be disposed of by environmentally acceptable means.
It is therefore an important object of this invention to provide a one-step process for the commercial production of C.sub.3 -C.sub.12 alkyl, substituted alkyl, alkenyl and cycloalkyl cyanoacetates in substantially quantitative yields based on the cyanoacetic acid starting material.
It is also an object of this invention to provide such an improved one-step process that is relatively economical to operate as compared to the processes of the prior art, both from the standpoint of equipment requirements and utilities consumed based on the amount of cyanacetate product produced.
It is yet another object of the invention to provide an improved reaction process with an efficient time-yield curve with little or no by-products that require processing for disposal.